Devices which functionally test integrated circuits having a large number of external terminals are already well known, such as, the LSI TEST SYSTEM described in the company bulletin, Fairchild Product Description, May 1981, No. 57148901. With respect to integrated circuits, the requirement exists on the part of the manufacturer, as well as on the user level, to identify defective products by systematic functional tests. For one, the manufacturer must ensure a high quality standard of its shipments for reasons of competitiveness and, secondly, it needs feedback data for its internal production process. The user, on the other hand, wants to pay only for perfect goods, wants to be able to judge the reliability of different suppliers and wants to avoid trouble in his own production as a result of defective parts received.
The achieved and further increasing complexity of integrated circuits (more and more functions are now being combined on a single semiconductor chip) requires, for technical and economic reasons, the automation of the testing process. The primary tool to automate the testing process is the use of electronic computers which control the running of testing programs for the integrated circuit test piece, for instance, in the case of digitally operating test pieces, defined sequences of bit patterns. With respect to the automation of the mechanical aspect of the testing process, the manual feeding of a test piece to a test station can be replaced by feeding devices and automatic handling devices.
A further practical problem goes hand in hand with the complexity of the integrated circuits: the large number of external terminals (pins) which are required for access to the highly integrated functions raises difficulties with arrangement and contacting with testing devices. A particular design problem arising therefrom, especially in a testing device for integrated circuits, is that the device which must be designed with largest dimensions on the one hand to accommodate the test pieces with the maximum amount of terminals which can be tested causes, on the other hand, the device to operate uneconomically when test pieces with a relatively small number of external terminals are tested. This problem cannot be remedied by having available a multiplicity of test heads designed in graduated stages at the testing station since a plurality of these expensive system components would be idle for most uses.
It is therefore an object of the invention to make a device of the type mentioned at the outset so flexible and economical that test pieces with the most different number of terminals can be tested, utilizing the existing testing capacity, namely, the number of test piece terminals that can be accomodated by the test heads, to the fullest.